class uuid {
    // 生成随机字符串
    static uuid(length) {
        var s = [];
        var hexDigits = "qwertyuiopasdfghjklzxcvbnm";
        // var hexDigits = "0123456789qwertyuiopasdfghjklzxcvbnm";
        for (var i = 0; i < length; i++) {
            s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
        }
        // s[14] = "4";  // bits 12-15 of the time_hi_and_version field to 0010
        // s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);  // bits 6-7 of the clock_seq_hi_and_reserved to 01
        // s[8] = s[13] = s[18] = s[23] = "-";
        var uuid = s.join("");
        return uuid;
    }
    static get_uuid(){
        let uid = uuid.uuid(5)
        let flag = true
        while (flag){
            if(this.uuid_list.indexOf(uid) == -1){
                this.uuid_list.push(uid)
                flag = false
            }else{
                uid = uuid.uuid(5)
                flag = true
            }
        }
        return uid
    }
}
uuid.uuid_list = []
module.exports = uuid